Synthetic polymers based on compounds from the petrochemical industry had a considerable industrial impact in the middle of the 20th century. Despite the numerous advantages of these materials, two drawbacks still remain to be solved: use of renewable resources for their production, and recycling of them after use. Taking into account their intrinsic properties, polymers obtained from renewable resources have therefore become an important alternative and there have been many advances both from the standpoint of synthesis and of processing of these materials. They are used, moreover, for a large number of applications such as moulding, packaging or textiles.
Among the various polymers obtained from renewable resources, polylactic acid or polylactide (PLA) is one of the most commonly used. Taking into account the use of renewable resources, polymers such as PLA have received particular attention, notably for partly replacing certain articles and mouldings in polyvinyl chloride (PVC), which despite their good balance of properties have certain shortcomings from the standpoint of wettability or heat resistance.
However, these polymers obtained from renewable resources must also be used for moulding or injection moulding, to make objects that must meet certain criteria from the standpoint of their mechanical and physical properties. It therefore appears necessary to develop compositions comprising these polymers and containing at least one plasticizer and other additives in order to satisfy the required properties, such as flexibility, hardness, wettability, impact toughness or elongation. Moreover, and depending on policies regarding environmental protection, it is desirable for the plasticizer used to be phthalate-free.
It also appears desirable that the polymer composition should contain compounds for improving impact toughness. In this context, it was often found that the use of phthalate-free plasticizer altered the glass transition temperature (Tg) of the composition, which consequently affected the impact toughness.
Generally, it goes without saying that we wish to have a favourable effect on the environment and therefore that the aim is to replace PVC objects with objects manufactured from polymers obtained from renewable resources.
Moreover, it has become apparent that even compositions based on PVC have certain drawbacks such as insufficient elongation at break, or inadequate heat resistance or wettability, these last two properties being manifested, for the resultant objects, by the development of cracks or difficulty in being painted.
Moreover, at present, for certain mouldings, for example figurines, the polymer compositions from which they are produced should meet at least three criteria, namely significantly improved properties of elongation at break, because they must be able to withstand deformation without damage, which can be achieved if the elongation at break is above 200%, a Shore hardness A between 60 and 95 because they must remain stable, and wettability expressed by a surface tension above 34 dyn/cm so that they can easily be painted. Now, at present, the existing polymer compositions from which moulded objects or injection mouldings are produced do not provide all of these properties.
Moreover, it is highly desirable that polymer compositions intended for preparation of moulded objects, for example figurines, in addition should have a good balance of other mechanical and physical properties, namely as indicated below:                Shore hardness D<50;        heat resistance expressed by the storage modulus at 54° C.>20 MPa;        good impact toughness expressed by a ductility index >30%;        total fracture energy >8 Joule;        deflection >18 mm and        good temperature resistance without crazing.        
There is therefore a need to develop polymer compositions obtained from renewable resources meeting all these criteria simultaneously and allowing objects to be manufactured by the usual techniques of plastics processing.